The present invention concerns a tensioning and immobilization device of a tension roller for transmission of rotational movements. Such transmission may be performed by flat belts, synchronous toothed belts, V belts; round or grooved belts; by single or multiple chains; by a cable or the like. The device according to the invention is a roller with an eccentric internal pivot mounted on a bearing surface of, for example, the support of the transmission.
An immobilization device for a belt tensioning roller enabling fixing the hub of an eccentric-forming roller in an angular position determined relative to a bearing surface, such as one which is part of a housing, a cylinder head, etc., is already known, specifically in French Patent No. 2,665,498.
This fixation of the hub is implemented- by means of a screw passing through the hub parallel to its axis of rotation to be screwed into the bearing surface. In this type of device, the shank of the aforementioned screw has on part of its length a smooth surface forming the axis of rotation of the hub of the roller. This hub can be rotated by means of an appropriate tool which engages in an opening provided on the surface of the roller opposite that designed to be in contact with the bearing surface. A fitting designed to accommodate the belt is mounted on a ball bearing, so as to turn freely around the hub. The interest of this device lies primarily in its minimal space requirement, resulting from the fact that the tensioning mechanism is internal to the roller.
Putting the roller into service consists of driving the hub of the roller, in rotation, around the shank of the screw until it assumes an angular position determined on the basis of the belt tension selected; then, in a second step, of fixing the hub in this position by tightening the clamping screw.
This device, with a small space requirement, has, however, three disadvantages:
the adjustment stroke is short because it is associated with the value of the eccentricity, which is in turn limited by the passage of the fixation screw inside the interior diameter of the ball bearing.
the tensile load of the transmission can be applied only with the help of a special wrench, placed in notches on the upper surface of the hub. The device, entirely cylindrical, does not permit the use of off-the-shelf wrenches.
measurement of the tensile load can be performed only indirectly, when the device is stopped, in three ways:
1) by measuring the elongation of the belt after tension,
2) by measuring the path of deflection of the belt after tension,
3) by measuring the frequency of vibration of the belt after tension using a special apparatus.
These methods of measurement of the value of the tensile load are not very precise and are difficult to implement. They use special means, not included among the usual tools of an assembly or maintenance shop. They require several successive adjustments and measurements. They are not direct measurements and, consequently, are imprecise. These measurement methods do not permit transmission of torque under optimum conditions of service life, of drive quality, of sound level. The tensile load must be determined and applied with precision.
The device according to the invention makes it possible to remedy these disadvantages. In fact, it consists of a tension roller with an eccentric pivot. It has a very small space requirement, since its components remain always inside the external diameter of the roller. It is fixed on the transmission support, using a large screw. Its large diameter base gives it good rigidity. Its tensioning stroke is adequate for most applications. The stroke and the tensile load are implemented using off-the-shelf clamping tools on a lower driving arm or an upper driving arm integral with the hub. The choice of one or the other depends on constraints of space and accessibility. The tensile load exerted by the roller on the transmission can be simultaneously exerted and measured directly, using a torque wrench. The device can be put in place, adjusted, and clamped into position from above the transmission support. This device, by way of nonrestrictive example, can be produced with a diameter from approximately 20 mm to a diameter of more than 300 mm, making it possible to extend its field of application, from office equipment to industrial machines.
The device according to the invention consists, in effect, of an external roller, with a shape suited to all types of transmission which may constitute a pulley for a flat belt, a synchronous toothed belt, a V belt, a round or grooved belt; a geared wheel for a single or multiple chains; a pulley for a cable. This roller accommodates one or a plurality of rotational guide fittings, which are integral to a hub which includes, according to a first characteristic, a clamping screw passing through the hub which acts on an intermediate part placed freely in a housing of the hub, with this intermediate part enabling the creation of a lateral offset between the axis of the clamping screw and a fixed pivot pin integral with the transmission support, with this fixed pivot pin consisting of a cylindrical portion constituting the rotation guidance of the hub, with a height defined between two faces, one of which rests on the bearing surface and the other is performed by the bottom of a cylindrical head which extends radially beyond the cylindrical part and which engages freely in a housing provided in the hub, with the distance between centers of the axes obtained by the aforementioned lateral offset enabling, by the rotation of the hub around the fixed pivot pin, when the clamping screw is not yet tightened, making the hub travel a circular path which constitutes the tensioning stroke of the device, the tightening of the clamping screw in the intermediate part, which acts as a flange and is supported at one of its ends, which has a projection, in the bottom of the housing and at the other end under the head of the fixed pivot pin, immobilizing the hub of the bearing surface by pressure and adhesion in the position determined.
The fixed pivot pin is eccentric relative to the axis of rotation of the roller but remains within the space occupied by the hub. The disassociation of the pivot pin and the clamping screw makes it possible to obtain maximum eccentricity while keeping all the components inside the external diameter of the roller. The self-locking nature and the stability of the unit is ensured by the large-diameter base of the hub. Since the face opposite the mounting surface on the transmission support is often inaccessible due to its shape, the presence of reinforcements, gussets, or mechanical elements, the installation and adjustment of the device can be carried out on the bearing surface of the transmission support, from above the tensioning device.
The device can be installed inside or outside the transmission.
According to a second characteristic, the hub has, in its base, a housing accommodating a lower driving arm integral with the hub, extending beyond the exterior of the base of the hub enabling, with the use of an off-the-shelf wrench or a torque wrench, pivoting the device around the fixed pivot pin and thus applying tension to the transmission.
The use of a torque wrench makes it possible to simultaneously apply and measure the force exerted and to thus obtain a specific, reproducible transmission tension.
According to a third characteristic, the hub has, in its upper part, a housing accommodating an upper driving arm integral with the hub, enabling, with the use of an off-the-shelf wrench or a torque wrench, pivoting the device around the fixed pivot pin and thus applying tension to the transmission.
The use of a torque wrench makes it possible to simultaneously apply and measure the force exerted and to thus obtain a specific, reproducible transmission tension.
According to another characteristic of the invention, the lower driving arm and the upper driving arm have ends adapted to accommodate additional devices for adjustment and position immobilization of the hub of the roller, devices for pulling or pushing by flexible or elastic elements, devices for pulling or pushing by remote control actuators, and control and safety devices detecting defects in the tensile load or in the angular position of the tension roller.
According to another characteristic of the invention, the intermediate part has no projection, the clamping screw holds said intermediate part in the bottom of the housing of the hub in a defined position permitting free pivoting of the intermediate part under the head of the fixed pivot pin and, consequently, free pivoting and sliding of the hub on the bearing surface, with the tensile load obtained by the action of a device for pushing or pulling acting on one or the other of the two driving arms.
According to another characteristic of the invention, the intermediate part consists, on the one hand, of a guide sliding in a housing of the hub parallel to the axis of rotation of the roller and, on the other, of a perpendicular flange extending from the guide supported against the head of the fixed pivot pin, which immobilizes the hub against the bearing surface by pressure and adhesion in the position determined, at the time of the tightening of the screw.
According to another characteristic of the invention, when the fixation of the device from below the transmission support is desirable, the intermediate part may have an internal screw thread accommodating the fixed pivot pin accessible from below the bearing surface which has an opening accommodating the cylindrical portion of the pivot pin, with the head of said pin being supported under the support of the transmission, with the tightening of the clamping screw ensuring immobilization by pressure and adhesion of the hub on the bearing surface.
According to another characteristic of the invention, the intermediate part is extended beyond the exterior of the base of the hub and constitutes the driving arm enabling exertion of the tensile load.
According to another characteristic of the invention, the lower driving arm, when it consists of a specific part, is removable and can be removed from the base of the hub by sliding in its housing, after adjustment of the tension of the transmission.
According to another characteristic of the invention, the lower and upper driving arms have, at their end, a protruding part with a polygon shape enabling the use of off-the-shelf clamping tools: open-end wrench, box wrench, ring wrench, adjustable wrench, socket wrench, torque wrench.
According to another characteristic of the invention, the intermediate part, when it is extended beyond the exterior of the base of the hub and constitutes the drive arm, has at its end a polygon-shaped protruding part enabling the use of off-the-shelf clamping tools: open-end wrench, box wrench, ring wrench, adjustable wrench, socket wrench, torque wrench.
According to another characteristic of the invention, the upper driving arm has a bore accommodating a pin concentric to the fixed pivot pin enabling, by means of a support integral with the transmission support, holding the end of the hub.